1. Field of the Invention
The present invention relates to a mobile communication terminal apparatus and a transmission apparatus. More particularly, the present invention relates to a mobile communication terminal apparatus and a transmission apparatus which employ a communication method which requires adjustment of a transmission output level.
2. Description of the Background Art
In digital mobile communication techniques, such as WCDMA (Wideband Code Division Multiple Access) and the like, a transmission output level of each mobile telephone terminal apparatus needs to be adjusted so that a base station can receive a signal having a constant strength irrespective of a distance between the base station and the mobile telephone terminal apparatus.
FIG. 12 is a diagram illustrating a base station 200 having a cell range 210 having a radius of about several tens of kilometers (e.g., about 30 km), and mobile telephone terminal apparatuses 100. The transmission output level of the mobile telephone terminal apparatus 100 needs to be increased with an increase in the distance from the base station 200 so that the base station 200 receives a signal having a constant strength when the communication environment is the same at any place within the cell range 210.
In order to achieve such a transmission output control, the mobile telephone terminal apparatus 100 needs to be equipped with a gain adjuster, such as a power amplifier, an attenuator or the like. In communication techniques, such as WCDMA and the like, since the dynamic range is broad, the mobile telephone terminal apparatus 100 needs to be equipped with a plurality of gain adjusters.
FIG. 13 is a block diagram illustrating an exemplary structure of a conventional mobile telephone terminal apparatus 100 which is disclosed in Japanese Patent Laid-Open Publication No. 2000-165311. The mobile telephone terminal apparatus 100 comprises an amplification section 113 including a power amplifier 102 and a power amplifier 103, a duplexer 104, an antenna 105, a low noise amplifier 112, a control logic section 111, and switches 106 to 110. In the case of transmission, an audio signal input to an input section 101 is amplified in the amplification section 113, and the resultant signal is transmitted via the duplexer 104 and from the antenna 105 to the base station 200.
The power amplifiers 102 and 103 are each used while the magnitude of a gain thereof is fixed. The magnitude of a gain of the amplification section 113 is determined, depending on which of the power amplifiers 102 and 103 is used. The power amplifiers 102 and 103 are selected by switching connections of the switches 106 to 110. An operating state of the amplification section 113 can be switched between the case where none of the power amplifiers 102 and 103 is used, the case where only the power amplifier 102 is used, and the case where both the power amplifier 102 and the power amplifier 103 are used.
In addition to the mobile telephone terminal apparatus 100 of FIG. 13, another mobile telephone terminal apparatus may be used in which power amplifiers having different gains are connected in parallel, and among them, a power amplifier to be used is selected, depending on the transmission output level.
In order to control the transmission output level within a broad range of as large as 80 dB so as to meet a communication standard, an attenuator or a variable gain amplifier, such as, for example, those described in U.S. Pat. No. 4,890,077, may be provided preceding the input section 101.
In this case, a gain which is largely and discontinuously changed by switching the power amplifiers 102 and 103 can be combined with a gain of an attenuator or the like which can be adjusted to any magnitude within a gain width of, for example, 40 dB, thereby obtaining any gain within a range of as large as 80 dB. Hereinafter, switching of the power amplifiers 102 and 103 is referred to as operation switching (consumed current switching).
A control section, such as the control logic section of FIG. 13 or the like, determines a target value of the transmission output level based on a strength of a received signal, compares the target value with an actual transmission output level, and based on a result of comparison, determines a gain to be adjusted, thereby controlling a gain of an amplifier or an attenuator. By such a feedback control, the transmission output level is adjusted, depending on a communication situation.
In order to change the transmission output level continuously, a gain of the whole circuit needs to be changed continuously. Therefore, when operation switching is performed, the gains of the attenuator and the like as well as the amplification section 113 need to be adjusted so that the gain of the whole circuit is not changed between immediately before and immediately after switching.
In order that the gain of the whole circuit is not changed between immediately before and immediately after switching, the switches 108 to 110 included in the amplification section 113 of FIG. 13 need to be controlled with the same timing. Further, the amount of attenuation of the attenuator and the like needs to be adjusted with the same timing as that of control of the switches 108 to 110 so that a gain which is largely changed in the amplification section 113 due to operation switching is canceled.
However, the control timings of the power amplifier and the attenuator may be deviated from each other due to a time delay of the feedback control or the like. Particularly, in the case of operation switching in the amplification section 113, a disturbance occurs in the transmission output level as illustrated in FIG. 14. More specifically, during operation switching, for example, instantaneously, a certain power amplifier is in a post-operation switching state, while another power amplifier or an attenuator is in a pre-operation switching state. At this instant, the gain of the whole circuit is deviated from a predetermine value, resulting in a disturbance in the transmission output level. Note that, in FIG. 14, it is assumed that operation switching is performed when the distance between the base station and the mobile telephone terminal apparatus is D3 (where the transmission output level is set to be 12 dBm).
In conventional mobile telephone terminal apparatuses, there are a number of types of voltages to be adjusted for adjustment of a gain. Therefore, the adjustment of each gain adjuster is complicated when a sudden change in power source voltage or a variation in set voltage occurs. Particularly when operation switching is performed, the attenuation amount of the attenuator needs to be largely changed. Therefore, when a sudden change in power source voltage occurs, the gain cannot be adjusted quickly to a desired value, so that a disturbance occurs in the output until the desired value is obtained.
When the transmission output level is disturbed, the strength of a received signal of the base station 200 is deviated from a standard value, so that a level difference occurs between adjacent channels, leading to a deterioration in audio quality, such as, for example, a disturbance occurs in an audio signal. In the case of actual communication, a communication situation is changed from moment to moment, such as the location of the mobile telephone terminal apparatus is changed; the mobile telephone terminal apparatus enters behind a building; or the like. Therefore, the operation switching of the amplification section 113 is frequently performed. Therefore, the disturbance of the transmission output level which occurs during operation switching needs to be suppressed in order to improve audio quality.